EP0579891B1 - Schaltung zur Ausführung einer Impedanz für die Sprechschaltung eines Fernsprechapparat - Google Patents

Schaltung zur Ausführung einer Impedanz für die Sprechschaltung eines Fernsprechapparat Download PDF

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Publication number
EP0579891B1
EP0579891B1 EP92830401A EP92830401A EP0579891B1 EP 0579891 B1 EP0579891 B1 EP 0579891B1 EP 92830401 A EP92830401 A EP 92830401A EP 92830401 A EP92830401 A EP 92830401A EP 0579891 B1 EP0579891 B1 EP 0579891B1
Authority
EP
European Patent Office
Prior art keywords
filter
circuit
signal
amplifier
telephone
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
EP92830401A
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English (en)
French (fr)
Other versions
EP0579891A1 (de
Inventor
Luciano Tomasini
Rinaldo Castello
Pietro Erratico
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
STMicroelectronics SRL
Original Assignee
STMicroelectronics SRL
SGS Thomson Microelectronics SRL
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by STMicroelectronics SRL, SGS Thomson Microelectronics SRL filed Critical STMicroelectronics SRL
Priority to EP92830401A priority Critical patent/EP0579891B1/de
Priority to DE69228807T priority patent/DE69228807T2/de
Priority to US08/095,752 priority patent/US5459787A/en
Priority to JP18150993A priority patent/JP3659982B2/ja
Publication of EP0579891A1 publication Critical patent/EP0579891A1/de
Application granted granted Critical
Publication of EP0579891B1 publication Critical patent/EP0579891B1/de
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04M—TELEPHONIC COMMUNICATION
    • H04M1/00—Substation equipment, e.g. for use by subscribers
    • H04M1/58—Anti-side-tone circuits
    • H04M1/585—Anti-side-tone circuits implemented without inductive element
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/38—Transceivers, i.e. devices in which transmitter and receiver form a structural unit and in which at least one part is used for functions of transmitting and receiving
    • H04B1/40—Circuits
    • H04B1/54—Circuits using the same frequency for two directions of communication
    • H04B1/58—Hybrid arrangements, i.e. arrangements for transition from single-path two-direction transmission to single-direction transmission on each of two paths or vice versa
    • H04B1/586—Hybrid arrangements, i.e. arrangements for transition from single-path two-direction transmission to single-direction transmission on each of two paths or vice versa using an electronic circuit
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04M—TELEPHONIC COMMUNICATION
    • H04M1/00—Substation equipment, e.g. for use by subscribers
    • H04M1/738—Interface circuits for coupling substations to external telephone lines
    • H04M1/76—Compensating for differences in line impedance

Definitions

  • This invention relates to a circuit for synthesizing an impedance associated with a telephone subscriber's circuit connected to a two-wire telephone line.
  • the field of application of this invention relates, in particular but not solely, to telephone speech circuits incorporated to telephone subscriber's appliances, and the description which follows will make reference to said field of application for simplicity of illustration.
  • each telephone company sets a maximum value of so-called return loss on the telephone band, and this value imposes a predetermined maximum admissible value on the termination impedance.
  • a telephone speech circuit provides for conversion from two to four wires, and that the accuracy of this conversion is tied, in turn, to the accuracy in value of another impedance, called balance impedance, which may be different from the termination impedance.
  • the termination and balance impedances are currently provided by a complicated structure, external of the integrated telephone circuit, which employs, moreover, comparatively expensive precision components.
  • the integrated circuit requires additional pins for making the various connections involved.
  • This prior art approach provides for the termination and balance impedances to be implemented basically by a precision external resistance.
  • This resistance is transformed into a complex impedance by means of a control circuit, internal of the integrated speech circuit, which is operated in accordance with an appropriate transfer function.
  • more external components are used additionally to the aforesaid resistance, namely: two coupling capacitors, two transistors, one diode, and a second resistance.
  • circuits for synthesizing an impedance associated with a telephone subscriber's circuit connected to a telephone line having a pair of terminals known from the prior art are given by US-A-4 558 185 and Patent Abstracts of Japan, vol. 14, no. 387 (E-967), 21.8.90 & JP-A-21 42 227.
  • the underlying technical problem of this invention is to provide an impedance synthesizing circuit which has such structural and functional characteristics as to overcome the above-mentioned disadvantages of the prior art.
  • a circuit embodying this invention for synthesizing an impedance associated with a telephone speech circuit 2.
  • the circuit of this invention is adapted to synthesize a complex impedance which can function both as a termination impedance and a balance impedance.
  • the telephone circuit 2 is a monolithically integrated type connected to a two-wire telephone subscriber's line having a pair of terminals L+ and L-.
  • the first of said terminals designated L+
  • the telephone signal receiving terminal and the other terminal, L-, represents a signal reference.
  • the circuit 1 of this invention is a positive feedback loop structure, at the first terminal L+ of the line 3, and comprises a single precision resistance R connected serially to the line and having one end connected to said first terminal L+.
  • the circuit 1 further comprises a first filter 12 having a first input 11 which is connected directly to the line terminal L+ and receives the telephone signal present on the line 3.
  • This filter 12 is essentially a capacitive coupler, and has a second input 10 connected to the other line terminal L-.
  • Component 12 comprises an internal antialias filter effective to remove high-frequency signals and avoid intermodulation noise of the signals being input to the circuit 1.
  • a second, zero-pole filter 8 is provided after the filter 12 which is connected centrally in the circuit 1 and has an output connected to the input of an amplifier 7 whose gain can be adjusted to suit the subscriber's demands.
  • the gain g of amplifier 7 has been selected to be 1.5.
  • the second filter 8 handles a sampled signal and is of a type known commercially as a switched capacitor. This filter type affords the required degree of accuracy for the impedance value, whilst involving no external calibration steps.
  • filter 8 affords best dynamic range for the power supply value (about 3 Volts) available to the telephone circuit 2.
  • the structure of circuit 1 further includes a block 5, connected after the amplifier 7 and having an output 4 connected to the other end of the precision resistance R.
  • This output 4 is characterized by a very low impedance.
  • Said block 5 is essentially a unit gain amplifier of the type referred to as driver/smoothing, that is functioning as a low-pass filter as well as a driver for the resistance R.
  • An input 6 of the filter/amplifier 5 is connected to the other line terminal L- to have the same signal reference as the first filter 12.
  • the feedback loop formed by the circuit 1 exhibits high stability resulting from the selection of a positive feedback associated with a loop gain which is at all times less than unity. This makes for a stable circuit irrespective of the value of the line impedance across the terminals L+ and L-.
  • the circuit of this invention obviates this problem by having the line voltage-driven, that is at a low impedance.
  • Vr V (1 - H(s)) where, H(s) is the transfer function from the input 11 of filter 12 to the output 4 of block 5.
  • the transfer function H(s) varies with the frequency of the telephone band, then it can be inferred that the resultant impedance across the terminals L+ and L- is a complex impedance, even if it has been generated by a single discrete component consisting of the resistance R.
  • impedance value may be changed as required by acting on the form of the transfer function of filter 8 and/or the gain of amplifier 7.
  • the circuit 1 may be provided with an external read-only memory, e.g. of the EPROM type, wherein various transfer function forms of the filter 8 can be stored.
  • the filter 8 could be "programmed" through a serial bus under control by a microprocessor.
  • Figure 2 shows diagramatically the circuitry that implements both the termination and the two-to-four wire conversion with balance and sidetone suppression.
  • a summing node 9 is connected between the amplifier 7 and the filter/amplifier 5 to receive both the signal from the amplifier 7 and a second, outgoing signal from another amplifier 13, in this case a unit gain one.
  • the last-named amplifier, 13, is connected after a second filter 15 of the switched capacitor type.
  • the filter 15 and amplifier 13 are designed to supply a precise gain and a flat frequency response within the telephone band of interest and in the presence of a nominal line impedance across the terminals L+ and L-.
  • a second circuit node 14 with subtractor function receives, at one end, a signal TX which is also input to the filter 15, and at the other end, the receive signal picked up after the antialias filter 12; TX being the signal to be transmitted following appropriate amplification.
  • the sidetone suppression can be effected quite simply by subtracting the receive signal from signal TX at the node 14.
  • the receive signal might require scaling through an amplifier.
  • the antialias filter 12 additionally to filtering out any noise from the line exceeding 80 kHz, will uncouple the impedance control loop at frequencies below 5 kHz. This uncoupling is necessary to hold the DC duty point fixed of the blocks which make up the control loop, regardless of the line length which defines said DC duty point.
  • the circuit of this invention does solve, in its various embodiments, the technical problem and affords a number of advantages, outstanding among which is the use of a single external component of a discrete kind, i.e. the resistance R.

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  • Engineering & Computer Science (AREA)
  • Signal Processing (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Interface Circuits In Exchanges (AREA)

Claims (5)

  1. Schaltung zum Synthetisieren einer einer Femsprechieilnehmerschaltung, die mit einer ein Paar von Anschlüssen aufweisenden Telefonleitung verbunden ist, beigegebenen Impedanz, die innerhalb einer Miikopplungsschleife aufweist:
    einen einzigen Präzisionswiderstand (R), der in Reihe mit einem Anschluß (L+) der Leitung (3) geschaltet ist:
    mindestens ein Schaltkondensator-Abtastfilter (8) mit einem mit dem Anschluß (L+) der Leitung verbundenen Eingang. der ein Telefonsignal empfängt; und
    einen zwischen das Filter (8) und den Widerstand (R) geschalteten Verstärker (7);
       gekennzeichnet durch:
    ein Paar zusätzlicher Filter (12, 5), wobei ein erstes Filter (12) der zusätzlichen Filter in die Mitkopplungsschleife geschaltet ist um ein Signal von dem Anschluß (L+) zu empfangen und zum Liefern eines Ausgangssignals für das Abtastfilter (8), wobei ein zweites Filter (5) der zusätzlichen Filter ein Tiefpaßfilter ist das ein Signal von dem Schaltkondensatorfilter (8) empfängt und zwischen den Verstärker (7) und den Widerstand (R) mit einem an ein Ende des Widerstandes (R) angeschlossenen Ausgang (4) geschaltet ist, wobei ein zweiter Ausgang (6) des zweiten Filters (5) der zusätzlichen Filter in einer Rückkopplungsbeziehung mit dem Eingang (10) des ersten Filters (12) über einen zweiten Anschluß (L-) der Leitung (3) verbunden ist.
  2. Schaltung nach Anspruch 1, dadurch gekennzeichnet, daß der Verstärker einen Verstärkungsfaktor von 1,5 aufweist.
  3. Schaltung nach Anspruch 1, dadurch gekennzeichnet, daß sie einen Summierungsknoten (9) aufweist, der dem Verstärker (7) nachgeschaltet ist und der ein Signal von einem zweiten Verstärker (13) empfängt, der nach der Art einer Kaskade mit einem zweiten Tiefpaßfilter (15) verbunden ist, wobei der zweite Filter (15) ein zu übertragendes Signal (TX) als Eingang enthält.
  4. Schaltung nach Anspruch 3, dadurch gekennzeichnet, daß sie einen Substrahierungsknoten (14) aufweist, der auf der einen Seite das zu übertragende Signal (TX) und auf der anderen Seite ein von dem Eingang des ersten Nullpolfilters (8) aufgenommenes Signal zum Unterdrücken jeglichen Auftretens von Echoerscheinungen empfängt.
  5. Schalrung zum Synthetisieren einer einer Fernsprechteilnehmerschaltung, die mit einer ein Paar von Anschlüssen aufweisenden Telefonleitung verbunden ist beigegebenen Abschluß- und Ausgleichsimpedanz, die innerhalb einer Mitkopplungsschleife aufweist:
    einen einzigen Präzisionswiderstand (R), der in Reihe mit einem Anschluß (L+) der Leitung (3) geschaltet ist:
    mindestens ein Schaltkondensator-Abtastfilter (8) mit einem mit dem Anschluß (L+) verbundenen und ein Telefonsignal empfangenden Eingang;
    einen zwischen das Filter (8) und den Widerstand (R) geschalteten Verstärker (7);
       gekennzeichnet durch:
    einen zweiten Verstärker (13), der mit einem zweiten Tiefpaßfilter (15) in Reihe geschaltet ist; und
    einen Summierknoten (9), der mit den entsprechenden Ausgängen der Verstärker (7, 13) und einem Ende des Widerstandes (R) verbunden ist;
    einen Rückhörunterdrückungs-Subtraktionsknoten (14), der auf der einen Seite mit dem Eingang des zweiten Filters (15) verbunden ist welches ein zu übertragendes Signal (TX) empfängt, und der auf der anderen Seite mit dem Eingang des ersten Filters (8) verbunden ist.
EP92830401A 1992-07-22 1992-07-22 Schaltung zur Ausführung einer Impedanz für die Sprechschaltung eines Fernsprechapparat Expired - Lifetime EP0579891B1 (de)

Priority Applications (4)

Application Number Priority Date Filing Date Title
EP92830401A EP0579891B1 (de) 1992-07-22 1992-07-22 Schaltung zur Ausführung einer Impedanz für die Sprechschaltung eines Fernsprechapparat
DE69228807T DE69228807T2 (de) 1992-07-22 1992-07-22 Schaltung zur Ausführung einer Impedanz für die Sprechschaltung eines Fernsprechapparat
US08/095,752 US5459787A (en) 1992-07-22 1993-07-21 Circuit for the implementation of an impedance for a telephone speech circuit
JP18150993A JP3659982B2 (ja) 1992-07-22 1993-07-22 電話音声回路に伴うインピーダンス実現回路

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
EP92830401A EP0579891B1 (de) 1992-07-22 1992-07-22 Schaltung zur Ausführung einer Impedanz für die Sprechschaltung eines Fernsprechapparat

Publications (2)

Publication Number Publication Date
EP0579891A1 EP0579891A1 (de) 1994-01-26
EP0579891B1 true EP0579891B1 (de) 1999-03-31

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EP92830401A Expired - Lifetime EP0579891B1 (de) 1992-07-22 1992-07-22 Schaltung zur Ausführung einer Impedanz für die Sprechschaltung eines Fernsprechapparat

Country Status (4)

Country Link
US (1) US5459787A (de)
EP (1) EP0579891B1 (de)
JP (1) JP3659982B2 (de)
DE (1) DE69228807T2 (de)

Families Citing this family (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0581373A2 (de) * 1992-07-31 1994-02-02 Koninklijke Philips Electronics N.V. Endstelle für drahtgebundene Fernübertragung
EP0581372A2 (de) * 1992-07-31 1994-02-02 Koninklijke Philips Electronics N.V. Endstelle zur drahtgebundenen Telekommunikation
US5598467A (en) * 1994-12-09 1997-01-28 National Semiconductor Corporation Signal interface circuit with selectable signal interface parameters
EP0739120B1 (de) * 1995-04-11 2001-06-06 STMicroelectronics S.r.l. Sprechschaltung für eine Fernsprechstelle
US7020274B1 (en) 2000-04-26 2006-03-28 Agilent Technologies, Inc. Universal apparatus and method for interfacing signals with telephony networks
US7130412B2 (en) 2001-11-29 2006-10-31 Adtran, Inc. Telecommunication line driver having synthesized output impedance derived from output current sensing circuit

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5895488A (ja) * 1981-12-02 1983-06-07 Hitachi Ltd ライン回路
US4567331A (en) * 1983-12-22 1986-01-28 Itt Corporation Electronic hybrid having synthesized impedance circuitry
EP0434950A3 (en) * 1989-12-23 1992-07-22 Standard Elektrik Lorenz Aktiengesellschaft Simulation of a complex impedance and interface for same

Also Published As

Publication number Publication date
EP0579891A1 (de) 1994-01-26
JPH06244930A (ja) 1994-09-02
DE69228807T2 (de) 1999-08-12
DE69228807D1 (de) 1999-05-06
US5459787A (en) 1995-10-17
JP3659982B2 (ja) 2005-06-15

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